1. Field of the Invention
The present invention relates to closing of a bore in a subsea well element. In particular the invention can be employed with a tree cap arranged on the spool of a Xmas tree.
2. History of the Related Art
In the field of oil and gas wells, there is known various ways to seal off a bore of a tubular well element, such as the bore of a Xmas tree. For instance, for subsea wells it is known to arrange a tree cap on top of the Xmas tree spool. The tree cap comprises a stinger which is inserted into the bore of the Xmas tree. In some cases, the Xmas tree spool comprises a production bore and a smaller annulus bore.
Furthermore, some Xmas trees are used for injection wells used to inject fluid into the well bore. The tree cap may then comprise two stingers, of which one is inserted into each of these bores.
It is also known to seal off bores with other bore barrier arrangements, such as plugs which are provided with locking means. European patent application EP 0687801 describes a wireline plug with a metal-to-metal sealing, arranged to be locked in a bore with internal locking grooves. The plug has locking keys (4) arranged to engage with the locking grooves of the bore. An axially movable expander sleeve (3) provides radial movement of the locking keys when it is moved axially. The expander sleeve and the locking keys are provided with sliding faces of different inclination, providing different radial moving distances with respect to the axial moving distance of the expander sleeve, in dependence on the engaged inclined face.
In order to lock the stinger or cap in place, it is known to arrange radially movable dogs, which can engage with inner locking profiles in a bore. To move the dogs radially, it is known to slide a locking sleeve along their inner faces. The locking sleeve typically has an inclined face which moves the dogs radially outward when the sleeve is moved down. In order to move such a locking sleeve down, however, it is common to use a tool which, before moving the sleeve, has to be secured to the well arrangement. This is to prevent the tool from moving upward when forcing the locking sleeve down.
The movement of a locking sleeve is typically provided for by hydraulic pistons in the running tool or by providing linear movement with an ROV actuation device.